1. Field of the Invention
This invention relates to an engineering plastic composition with excellent flowability, heat stability, and desirable mechanical properties, and to articles made of the same.
2. Description of the Prior Art
Many resins are known as engineering plastic materials. They include polyetherimide, polyarylketone, aromatic polysulfone resin, polyarylenesulfide, polyarylate, saturated polyester (liquid crystal polyester), polyamide-imide, polycarbonate, polyphenylene oxide, polyamide, polyoxymethylene, etc. These engineering plastic materials can be used in various kinds of articles that require a high-performance material with qualities such as excellent heat stability and mechanical properties. However, in general, the melt viscosities of engineering plastic materials are high, and as a result, the workability of the materials is poor. Therefore, it is not easy to use these engineering plastic materials for products which must be formed with accuracy. For these reasons, there is a need for an engineering plastic composition that has a low melt viscosity, that is, satisfactory flowability, and workability, during molding.
In general, as methods by which the melt viscosity of polymers can be lowered, the following two methods have been adopted: (1) to decrease the molecular weight of the polymer, and (2) to add a plasticizer or to add a processing aid.
When the first method is used, the tensile strength, the impact strength, and other mechanical properties of the articles that are made of the polymer are worsened, and the heat stability of the articles declines. In the second method, many of the substances that can provide engineering plastic materials with plasticity have poor heat stability, so that these substances are not stable at the molding temperature for the engineering plastic materials. For these reasons, a plasticizer or processing aid that is effective with engineering plastic materials has not yet been found.
Many attempts have been made to improve the moldability or workability of engineering plastic materials. With respect to the engineering plastic materials listed above, the characteristics and the methods for the improvement of the moldability or workability will be described below in detail.
(a) Polyetherimide
Since polyetherimide has a high glass transition temperature of 217.degree. C., it is used as a thermoplastic resin with heat stability. However, the melt viscosity of polyetherimide is high, so the moldability is poor and it is not easy to use these engineering plastic materials for products which must be formed with accuracy.
In order to improve the moldability of polyetherimide, methods that involve the blending of polyetherimide with other thermoplastic resins have been proposed. For example, there are methods in which polyarylether with a low molecular weight is included in a blend (Japanese Laid-Open Patent Publication No. 59-12967), in which polyalkyl lactone with a molecular weight within specified limits is included in a blend (Japanese Laid-Open Patent Publication No. 60-156754), and in which a block copolymer made of vinyl aromatic compounds and diene compounds is included in a blend (Japanese Laid-Open Patent Publication No. 60-156753). However, compared to the heat stability of polyetherimide, the heat stability of all of these thermoplastic resins is low. Therefore, in these methods, the heat stability of the polyetherimide compound is decreased.
(b) Polyarylketone
Polyarylketone is used for applications which require high performance with qualities, as a thermoplastic resin with excellent heat, hydrolysis and solvent stability, and desirable mechanical strength. However, the melt viscosity of polyarylketone is also high, so it is not easy to use these engineering plastic materials for products to be formed with accuracy.
A method has been proposed in which the moldability of polyarylketone is improved by its being blended with polyphenylenesulfide (Japanese Laid-Open Patent Publication No. 57-172954). In this method, in order that the moldability will be improved sufficiently, it is necessary to include a large amount (tens of percents by weight based on the total weight of the resin) of polyphenylenesulfide in the blend. For this reason, the excellent mechanical properties of polyarylketone decline.
(c) Aromatic polysulfone resin
Aromatic polysulfone resin is used in various kinds of articles as a thermoplastic resin with excellent heat stability. However, the melt viscosity of aromatic polysulfone resin is also high, so the moldability is poor and it is not easy to use these engineering plastic materials for products which must be formed with accuracy.
In order to improve the flowability of resins, methods that involve the blending of the aforementioned resin with other thermoplastic resins have been proposed besides the aforementioned method. For example, there is a method in which polyurethane is blended with aromatic polysulfone resin (Japanese Laid-Open Patent Publication No. 50-144750); there is another method in which polyalkylene-phenylene ester or polyalkylene-phenylene ether is blended with aromatic polysulfone resin (Japanese Laid-Open Patent Publication No. 50-146648); there is still another method in which a copolymer of an aromatic vinyl monomer and maleimide monomer is blended with aromatic polysulfone resin (Japanese Laid-Open Patent Publication No. 61-66750); and there is a further method in which a copolymer of acrylonitrile, butadiene, and styrene is blended with aromatic polysulfone resin (Japanese Laid-Open Patent Publication No. 56-167752). The heat stability of all of the thermoplastic resins used in the above methods is inferior to that of aromatic polysulfone resin. For that reason, the excellent heat stability of the aromatic polysulfone resin is decreased by their use.
(d) Polyarylenesulfide
Polyarylenesulfide is a resin with excellent heat stability. Particularly, reinforced polyarylenesulfide, making use of the good affinity for various fillers and reinforcing fibers, has excellent mechanical properties, heat stability and electric properties. In order to improve the flowability of polyarylenesulfide, methods have been proposed in which solid polyethylene is added to polyarylenesulfide (Japanese Laid-Open Patent Publication No. 54-47752) and in which a block copolymer of hydrogenated conjugated dienes and aromatic compounds with one vinyl group is added to polyarylenesulfide (Japanese Laid-Open Patent Publication No. 59-217760). However, with these techniques, because the heat stability of the polymers used is inferior to that of the polyarylenesulfide, the superior heat stability of the polyarylenesulfide is decreased.
(e) Polyarylate
When polyarylate is prepared by polymerization, an agent for regulating the molecular weight is added, said agent being a monohydric aliphatic alcohol or an aliphatic monocarboxylic acid, and accordingly it is possible to obtain polyarylate with a comparatively low molecular weight. This method has been proposed (Japanese Patent Publication No. 57-49046). Other methods that have been proposed include a method in which a branching agent such as alcohol that has three or more hydroxyl groups is used (Japanese Patent Publication No. 61-26567). However, in such methods, the excellent mechanical and other properties of the polyarylate are worsened.
(f) Saturated polyester (Liquid crystal polyester)
Saturated polyester has excellent mechanical properties, heat stability, electrical properties, and the like. Particularly, liquid crystal polyester has excellent heat stability, high strength, excellent modulus of elasticity, and a low linear expansion coefficient, so it is used for parts such as machine parts and electrical parts which require high performance with these qualities. In order to improve the mechanical properties of polyester, a method has been proposed in which stiffeners such as reinforcing fibers or fillers are added to liquid crystal polyester. However, when these additives are added, the flowability is decreased. Therefore, it is necessary to raise the molding temperature when thin articles or articles with complex structures are molded, but resins are degraded during a prolonged heating in a molder with a high temperature and hence desirable molded articles cannot be obtained.
In order to improve the flowability of polyester, a method has been proposed in which a small amount of a liquid crystal compound of low molecular weight is blended with liquid crystal polyester (Japanese Laid-Open Patent Publication No. 59-85733). However, because the liquid-crystal transition temperature of liquid crystal compounds of low molecular weight is relatively low, the heat stability of the polyester is decreased.
(g) Polyamide-imide
Polyamide-imide has a high glass transition temperature of 280.degree. C.-290.degree. C., so it is used for applications which require high performance, as a thermoplastic resin with excellent mechanical properties at a high temperature. However, the melt viscosity of polyamide-imide is high, so it is necessary to mold at a high temperature of 320.degree. C.-350.degree. C. and the viscosity is prone to increase because of the molecular chain elongation reaction occurring when heating at 360.degree. C. or more. Therefore, it is not easy to use polyamide-imide for products which must be formed with accuracy.
In order to improve the flowability of polyamide-imide, a method has been proposed in which an aromatic aminocarboxylic acid or its derivative or else an aromatic diamine with one of its amino groups masked is added as an agent to regulate the molecular weight when polyamide-imide is polycondensed (Japanese Laid-Open Patent Publication No. 61-44928). However, although the moldability and workability of the polyamide-imide obtained by this method are good, the density of cross-linking caused by the reaction that takes place in the polyamide-imide during the time of post-curing is decreased, so that the excellent qualities of polyamide-imide cannot be maintained.
(h) Polycarbonate
Polycarbonate has a high glass transition temperature of 140.degree. C.-150.degree. C., and its mechanical properties, dimensional stability and transparency are extremely good. Because of its mechanical properties, heat stability and other qualities, polycarbonate is suitable for use in machine parts, electrical parts, optical parts, and other products in which high performance is needed. On the other hand, polycarbonate has excellent impact strength, but the problem is that the value of impact strength is prone to change with the thickness of the articles.
When polycarbonate is used as a resin in machine parts or electrical parts, in order to increase the mechanical properties of the part, reinforcing fibers such as glass fibers and fillers such as silica are added to the polycarbonate. However, the impact strength of a polycarbonate composition in which these are added generally decreases; and high temperatures of 300.degree. C.-360.degree. C. are needed in molding. If this composition is heated to 350.degree. C. or more, the product may be discolored.
Therefore, there is a strong need for a polycarbonate resin composition with low melt viscosity, that is, excellent flowability, excellent moldability, and high impact strength.
In order to obtain a polycarbonate resin composition with improved impact strength, a method in which .alpha.-olefin glycidyl(meth)acrylate copolymer is blended with polycarbonate (Japanese Laid-Open Patent Publication No. 61-44897) has been proposed. However, the problem is that the excellent heat stability of polycarbonate is greatly decreased. Besides the aforementioned method, another method in which polycarbonate is blended with other polymers has been proposed. Particularly, a mixture with polystyrene resins is most popular and acceptable on the market. For example, IUPILON.RTM. available from Mitsubishi Gas Chemical Company Inc., MALTILON.RTM. available from Teijin Kasei Corp., and NOVAMATE.RTM. available from Mitsubishi Kasei Corp. are commercially available. And if a new complex with polycarbonate is developed, a new market is opened up which is of very great importance.
(i) Polyphenylene oxide
Polyphenylene oxide (PPO resin) is an engineering plastic material with excellent heat stability. However, for reasons such as poor moldability and low impact strength, various methods have been proposed in order to solve the problems. For example, in order to improve the moldability of polyphenylene oxide, a method in which polyphenylene oxide is blended with other polymers has been proposed and polymerblended mixtures, for example, polyphenylene oxide/styrene or polyphenylene oxide/nylon are commercially available. For example, NORYL.RTM. and NORYL GTX.RTM. available from GE Corp., XYRON.RTM. available from Asahi Chemical Industry Co., Ltd., YUPIACE.RTM. available from Diamarl are known.
However, in a composition of polyphenylene oxide that contains a large amount of polystyrene or nylon, the moldability is improved but the heat stability is decreased. When glass fibers are added to these blends, the heat stability and mechanical properties of the mixtures obtained are excellent, but the flowability is poor and the moldability declines.
Other methods have also been proposed. For example, there is a method in which a copolymer of a vinyl aromatic compound and an unsaturated dicarboxylic anhydride is blended with polyphenylene oxide (Japanese Laid-Open Patent Publication No. 58-42648); there is another method in which polyalkylene glycol is blended with polyphenylene oxide (Japanese Laid-Open Patent Publication No. 59-20354); and there is still another method in which olefin groups and glycidyl(meth)acrylate copolymer is blended with polyphenylene oxide (Japanese Laid-Open Patent Publication No. 57-108153). In these methods also, however, the heat stability of the polyphenylene oxide is worsened.
(j) Polyamide
Polyamide has excellent mechanical properties, heat stability and wear resistance and is used, making use of these excellent properties, in various kinds of articles such as machine parts and electrical parts which require high performance. In order to further improve the mechanical properties of this resin, a method has been proposed in which stiffeners such as reinforcing fibers or fillers are added. However, when these additives are added, the flowability is decreased. Therefore, it is necessary to raise the molding temperature when thin articles or articles with complex structures are molded, but resins are degraded during the prolonged heating in a molder with a high temperature and hence desirable molded articles cannot be obtained.
(k) Polyoxymethylene
Polyoxymethylene has excellent mechanical properties, heat stability and dimensional stability, so it is widely used in parts such as machine parts, electrical parts, automotive parts, as an engineering plastic material with well-balanced properties.
Recently, according to various needs on the market, polyoxymethylenes suitable for each application have been developed. Complexation between polyoxymethylene and other resins is an effective means to change the properties. For example, in order to improve the impact strength of polyoxymethylene, polymer alloy in which polyoxymethylene is complexed with urethane thermoplastic elastomer is commercially available. A method in which a specific modified .alpha.-olefin polymer is blended with polyoxymethylene is disclosed in Japanese Laid-Open Patent Publication No. 59-204652, in order to improve the impact strength of polyoxymethylene. However, these methods decrease the heat stability of polyoxymethylene.
When polyoxymethylene is used as a resin in machine parts or electrical parts, in order to increase the mechanical properties of the part, reinforcing fibers such as glass fibers and fillers such as silica are added to the polyoxymethylene. However, the impact strength of a polyoxymethylene composition in which these are added, generally decreases; and, moreover, the flowability decreases. Therefore, it is necessary to mold at a high temperature but the resin is prone to degrade.
Therefore, there is a strong need for a polyoxymethylene composition with low melt viscosity, that is, excellent workability, excellent moldability, and high impact strength.